The physiological levels of molecular biomarkers can be regarded as time-varying continuous signals. However, clinicians seldom take advantage of this temporal information in making diagnostic and prognostic decisions. Biomarker measurements are often made at single time points, which do not adequately capture the dynamics of the underlying signal if they miss transient changes occurring between measurements. For instance, levels of serum cardiac troponin I (cTnI), creatinine kinase (the CK-MB isoform) and myoglobin elevate and return to baseline in a stereotyped manner after acute myocardial infarction (MI). A given measured value could correspond to either the early or late phase of biomarker release.
Most MIs are characterized by symptoms of severe discomfort. However, a significant minority, defined as unrecognized MIs, are accompanied by minimal or no symptoms. The 30-year follow-up of the Framingham Heart Study reported that 28% and 35% of MIs are unrecognized in men and women, respectively. Gutterman D. D. Silent myocardial ischemia, Circ. J. 73, 785-797 (2009). However, current standards for detecting unrecognized MIs rely primarily on electrocardiographic surveillance. Results vary markedly between such studies because of differing electrocardiographic criteria. Patients at high risk for unrecognized MIs are followed periodically by their cardiologists but MIs timed between these visits can go unnoticed.
Accordingly, it would be desirable to provide a sensor that reports on integrated MI biomarker levels throughout these intervals to identify these previously undetectable infarcts.